Fluid-powered linear actuators



Sept. 6, 1966 F. BRADBURY FLUID-POWERED LINEAR ACTUATORS Filed June 29, 1964 1 o W P f 5 @mn 5 N 0 P a a United States Patent FLUID-POWERED LINEAR ACTUATORS Farel Bradbury, Square Root, 32 Church St.,

Hampton, England Filed June 29, 1964, Ser. No. 378,911 Claims priority, application Great Britain, July 1, 1963, 26,088/ 63 4 Claims. (Cl. 92-113) This invention concerns improvements in or relating to fluid-powered linear actuators.

yIt is an object of this invention to provide an improved fluid-powered linear actuator, i.e. a hydraulically or pneumatically operated piston-and-cylinder device of the displacement type, either single or double acting. In particular, it is desired t-o make the speed of movement of the ram, that is to say of the piston relative to the cylinder, variable independently of the rate of entry or exit of lfluid to or from the cylinder, while using a simple, reliable and economic form of construction.

According to this invention there is provided a linear actuator of the displacement type, comprising a hydraulic or pneumatic cylinder member and a coacting piston and piston-rod member defining a chamber therebetween, One or more probe-receiving bores `opening into said chamber through the cylinder and/or piston end faces and disposed in or parallel to the main axis of the cylinder and piston, an open-ended generally tubular probe mounted freely `slidable in each said bore and capable of being substantially fully received therein, aud means for admitting pressure diuid into said chamber disposed in one of said end faces opposite each said bore, so that in operation the kinetic energy of admitted dluid is transmitted through the generally tubular probe to a pocket defined by the bore and its probe and converted to a static pressure which forces the probe from the bore to encircle the [fluid admission means and 4bear upon the opposed end face of the chamber, and means for permitting egress of pressure iluid from said chamber to collapse said actuator.

With the device of this invention it is possible while using a simple, reliable and economic form of construction to advance the ram rapidly on its `forward stroke to contact a workpiece and then immediately vary its action to exert a slow thrust employing the full hydraulic or pneumatic force, while the device can also optionally be capable of thereafter etfecting a reverse stroke of considerable rapidity so as to withdraw the ram quickly.

The cylinder and/or piston member(s) containing a probe-receiving fbore must be of an axial length sutiicient J to accommodate a bore of a depth adequate to receive substantially the entire length of the probe so that the actuator can be collapsed to its maximum extent. yBecause in most cases the piston rod can more readily accommodate a bore of the requisite depth than 4can either the cylinder end wall or the piston head, it is preferred that for at least the power stroke of the actuator the probe-receiving bore should extend through the piston head into the piston rod. With a double-acting actuator the probereceiving bore which functions on collapse of the cylinder may however be formed on the annulus side `of the piston.

The probe can be formed from any convenient rigid or semi-rigid material and provided it is of open-ended generally tubular construction may be of any cross-sectional shape dictated by convenience or necessity. Usually however the probe will be of uniformly annular crosssection, and thus cylindrical in overall external shape, while `obviously the bore will have a generally complementary shape.

The admission of pressure rfluid to the pocket dened by the ends of the probe .and bore can take place through Patented Sept. 6, i966 ice one or more ports in the end face of either the pist-on or the cylinder, as appropriate. Where as preferred the receiving bore is formed in the piston the pressure uid is then fed into the hollow probe through an entry port in the cylinder end face. To complete a fully adequate path for the fluid from the entry port in the cylinder end face through the hollow probe to the pocket, the free end of the probe must abut against the cylinder end face and encircle the entry port. To achieve this it surprisingly is not necessary for the hollow probe to be anchored to the cylinder end face about the entry port but instead it is a fundamental feature of the invention that the hollow probe should lloat freely within the bore, optionally biassed into engagement with the cylinder end face by means of a compression spring disposed within the pocket, but always with a portion disposed inside the receiving bore. The fluid path from the entry port to the pocket is simply completed by directing -fluid under pressure into the chamber through a nozzle which forms a jet directed at the open end of the hollow probe. Then, even though the probe at that instant may not be abutting against the face of the cylinder, the kinetic energy of the jet of pressure yfluid will be converted into a static pressure within the pocket which forces the probe out of its receiving bore to seat against the cylinder face, encircling the nozzle. Because of this arrangement, the probe need be neither anchored nor mounted, and thus problems of concentricity in manufacture are greatly alleviated.

The operation of a linear actuator in accordance with this invention will now be described. When the cylinder and piston combination of the actuator is in a fully collapsed condition, if pressure diuid is admitted to the pocket within the receiving bore via the hollow probe the latter will thereby be forced out of the receiving bore and, since its other end abuts against the `opposite end face of the cylinder or piston, the probe therefore thrusts against the opposite end face and thus causes relative motion between the piston and cylinder. The speed of movement thus imparted to the piston and cylinder combination is far greater than would be the case were an equal volume off liuid admitted to the main chamber, though of course the force is less.

During movement of the piston relative to the cylinder, under the trust of the probe, fluid naturally must also be supplied to the main cylinder chamber, but this may be drawn from a low-pressure or even a non-pressurised atmospheric source, conveniently `through a non-return or other valve. Similarly, the release of the fluid in the main chamber when the actuator is allowed to collapse can be accomplished by means of valves external to or built integral with the actuator. The hydraulic or pneumatic fluid controls and connections to the main cylinder may be of the single, the double-acting or the regenerative type.

Optionally, means may be provided whereby the fluid pressures in the main chamber and pocket may be equalised, particularly at stalled or low speeeds. Suitable i means include an orifice in the wall of the tubular probe or a gap or leakage path between the probe and the probe bore, for instance either in the form of a V-shaped or similar notch or channel extending longitudinally of the probe or bore, or by deliberately fitting the probe only very loosely within the bore. If it is desired positively to retract the ram at the greater speed made possible by this device so as to return the piston to the collapsed position within the cylinder, a probe can be provided which will operate in a probe bore, which bore has its opening in the main annular chamber of the cylinder. When the pressure fluid is admitted to the pocket at the end of the receiving bore the actuator will be rapidly advanced by the probe until the ram encounters a workpiece, but at this point free movement of the actuator will be restrained whereupon the greater pressure built up in the pocket will cause fluid to pass in quantity through the orifice or leakage path and allow the pressure to build up in the main chamber, thus slowing down the rate of advance of the ram but increasing its thrust, ultimately to the full force exertable by the linear actuator.

It should incidentally be noted that, since the operating characteristics of the actuator are determined by the rate at which the pressure fluid can communicate itself through the entry port to the probe, and then from the probe pocket to the main chamber via the orifce(s) and/ or leakage path(s) these operating characteristics can if desired be adjusted by altering the viscosity of the pressure uid employed.

In order that the invention may be well understood certain preferred embodiments thereof will now be described in greater detail, though by way of illustration only, with reference to the accompanying drawings, in which:

FIGURE 1 is a schematic axial cross-section through a simple double action type linear actuator having freelyfloating probes located on either side of the piston, and also diagrammatically shows the hydraulic connections to the actuator; and

FIGURE 2 is an enlarged schematic axial cross-sectional vew through a linear actuator employing a single oating spring-biassed probe.

Referring irst to FIGURE 1, the linear actuator 1 comprises a hydraulic cylinder 2 and a piston 3 carrying a piston rod 4. The piston is associated with open-ended generally tubular probes 5 and 6, one situated on each side thereof, and each slidably mounted within complementary receiving bore, indicated 7, 8 respectively. At the base of the bores 7 and 8 there is in each case a pocket indicated 9, 10 respectively, defined by the end of the respective probes and bores. Since the linear actuator is of the double action type, the piston 2 is surrounded by one main chamber 11 and by another main chamber 12. The probe 5 has an orifice 19 at its outer end and similarly the probe 6 has an orifice 13 at its outer end, through which orices hydraulic fluid may escape into respectively the main chamber 11 and the main chamber 12.

The cylinder 2 has in its end wall four ports 14, 15, 16 and 17 respectively. Ports 14 and 17, which face the tubular probes, are high pressure inlets, whereas ports 15 and 16 are outlet and low pressure inlet connections. All the ports may be suitably valved and high pressure inlet ports 14 and 17 are advantageously nozzle-shaped in order the better to direct a jet of uid from them through the facing probe. The nozzle shape is as shown at 23, FIGURE 2. The forward-stroke main chamber 11 is sealed olf from the reverse-stroke main chamber 12 by one or more annular piston sealing rings 18, mounted usually on the piston 3 but if desired in the wall of cylinder 2.

In operation on the forward stroke high pressure fluid enters the chamber 11 through inlet port 14 and passes via the interior of hollow probe 5 to the pocket 9 in the bore 7. Pressure is thus created in the pocket 9 which forces the probe 5 out of bore 7 to abut against the cylinder end wall of main chamber 11, with its tubular end encircling inlet port 14, and then as pressure is further built up in pocket 9 the probe 5 thrusts against the cylinder end wall, and the piston 3 is moved rapidly forward carrying with the piston rod 4 until the ram of the linear actuator is stalled by contact with the workpiece. During this rapid advance low pressure hydraulic fluid is admitted to the main chamber 11 and exhausted from main chamber 12 through inlet port 15 and outlet port 16 respectively, as will be described in more detail subsequently. When the ram is arrested or stalled, the pressure in the pocket 9 is transmitted to the main chamber 11, through lthe orifice 19 and/or along the annular leakage path between the probe 5 and bore 7 and builds up in chamber 11 until the full pressure is applied over the broad face of piston 3, thus exerting the full force of which the linear actuator is capable.

The arrangement of fluid transmission to the linear actuator 1 is also shown in FIGURE 1. The hydraulic uid is stored in low pressure reservoir 101, from which in operation it is pumped to a direction selector valve 102. According to the setting of valve 102, the pressurised liuid will pass either via inlet port 14 or port 17 into the main chamber 11 or 12 and thence, through probe 5 or 6 respectively, to the pockets 9 or 10 respectively. If the setting of the selector valve 102 is such as to pass pressurised iluid from the reservoir 101 to inlet port 14, then the setting of selector valve 102 will also be such as to allow fluid in chamber 12' to exhaust itself via port 17 to the reservoir 101, and vice versa.

Direction selector valve 102 is a four-way valve whose schematic construction is as shown in FIGURE 1 which is shown (by arrows indicating the direction of flow) with pistons 3 being advanced so that pressurised fluid is supplied to port 14 and fluid is exhausted through port 17 through valve 102. Pressurised fluid is supplied to valve 102 from reservoir 101 by a pump 104 via relief valve 105. Simultaneously, a further direction selector valve 103 coupled to and operating in synchronism with direction selector valve 102 operates to connect the reservoir 101 Via either port 15 or 16 to either chamber 11 or 12 respectively, dependent on the probe into which pressurised fluid is being passed. The schematic construction of valve 103 (which is `in two parts, 103A and 103B) is as shown in FIGURE 1, the two valves 103A and 103B being conventional preill or pilot oper-ated check valves. The direction of ow of fluid with piston 3 being advanced is again shown by arrows. Thus, with direction selector valve 102 set so that uid under pressure is being fed to port 14 while port 17 is Iconnected to exhaust, the direction selector valve 103 will set so that fluid from reservoir 101 is allowed to flow through valve 103B (while reduced pressure on the chamber 11 side of the valve is present to keep the valve open) into (but not out of) chamber 11 via port 15, while fluid is also allowed to be exhausted through valve 103A (under influence of pressurised uid supplied from valve 102) from chamber 12 via port 16 to the reservoir 101. It should be noted that the schematic arrangements for valves 102, 103A and 103B are each illustrative of one of several different types of valve which could be used for these purposes.

On the reverse stroke of the linear actuator, the direction selector valves 102, 103 are set in the alternative position, whereupon high pressure fluid enters port 17 to pass via probe 6 to the pocket 10 in the bore 8. Pressure created in the pocket 10 moves the probe 6 forward to encircle the port 17 and thrust against the end wall of the main chamber 12, withdrawing the piston 3 and the piston rod 4 out of contact with the workpiece. During this reverse stroke, direction selector valve 102 allows fluid to escape from main chamber 11 via port 14, and simultaneously direction selector valve 103 allows fluid to enter main chamber 12 from the reservoir 101 via port 16 and also to exhaust itself from main chamber 11 to the reservoir 101 via port 15. Consequently the reverse stroke of the linear actuator is carried out just as rapidly as was the forward stroke up to the moment that it was stalled by `contact with the workpiece.

Referring now to FIGURE 2 it will be seen that the construction is essentially similar to that of the embodiment illustrated in FIGURE 1, except that a single tubular probe 5 floats freely in bore 8, and is biassed out of bore 8 by a compression spring 20. In the cylinder end face 21 there is provided an entry port 22 having a nozzle 23 directed at the open end 24 of the freely floating probe 5. Then hydraulic fluid is forced under pressure through entry port 22, it passes through nozzle 23 and the jet thus formed travels through chamber 11, enters the open end 24 and passes along to pocket 9 where its kinetic energy is transformed into a pressure which, acting on the pocket end of probe 5 assists the spring 20 to force the probe out of the bore 8 until its chamber end seats against end face 21 encircling nozzle 23. It will be noted that the piston 3 (or piston sealing ring) is retained on the head of piston rod 4 by means of a screw-threaded retaining ring 25.

Other modifications may, of course, be made by those skilled in the art without departing from the scope of this invention. For instance, the number of probes and bores may be varied and also the distribution thereof between the various possible locations may be unequal, while both the probe(s) and the piston/ cylinder arrangement can if desired be telescopic in construction.

I claim:

1. A linear actuator of the displacement type comprising a `cylinder member and a coacting piston-and-rod member defining a hydraulic fluid chamber therebetween, means in one end face of said chamber defining at least one bore opening through said end face into said chamber and extending longitudinally in Ia direction parallel to the actuator axis, an open-ended generally-tubular probe freely-slidably mounted in said bore and capable of being substantially fully received therein, the end of said bore and said probe defining a probe pocket therebetween means for admitting pressurized hydraulic fluid into said chamber disposed in the opposite chamber end face through which hydraulic fluid can be fed into and through said open-ended probe, and means for admitting hydraulic fluid to said `chamber and for exhausting it therefrom on advance and withdrawal of the actuator respectively, so that in operation the kinetic energy of admitted pressurised fluid is transmitted through the generally-tubular probe to said pocket there to create a pressure which tends to force said probe from said bore to encircle said pressurised fluid admission means and bear upon the opposed chamber end face.

2. A linear actuator according to claim l, wherein the means defining the bore extend axially of the actuator through the piston and piston rod member.

3. A linear actuator of the displacement type comprising a cylinder member and a coacting piston-and-rod member defining a hydraulic fluid chamber therebetween, means in the piston end face defining an axially-extending cylindrical bore opening through said end face into said chamber, an open-ended tubular probe of length commensurate with said bore defining a pocket therebetween, a nozzled jet for admitting pressurized hydraulic fluid to said chamber disposed in said cylinder end face said nozzle being directed at the open end of said probe, and inlet and outlet connections for hydraulic fluid to admit and exhaust hydraulic fluid to and from said chamber on advance and Withdrawal of the actuator respectively, so that in operation the kinetic energy of the admitted pressurised fluid is transmitted through said probe to the pocket and creates -a pressure which forces the chamber end of said probe to bear upon the cylinder end face encircling the nozzled jet.

4. A linear actuator of the displacement type comprising a cylinder member and a coacting piston-and-rod member defining a hydraulic fluid chamber therebetween, means in the piston end face defining an axially-extending cylindrical bore opening through said end face into said chamber, an open-ended tubular probe of length commensurate with said bore mounted freely-slidably therein, the ends of said probe and bore defining a pocket therebetween, a compression spring disposed Within said pocket and bearing normally upon the respective ends of said bore and probe to urge the latter from the bore towards said chamber, an inlet port for admitting pressurized hydraulic fluid to said chamber disposed in the cylinder end face opposite said open-ended probe, and inlet and outlet connections for hydraulic fluid to admit and exhaust hydraulic fluid to and from said chamber -on advance and withdrawal of the actuator respectively, so that in operation the kinetic energy of the admitted pressurised fluid is transmitted through said probe to the pocket and creates a pressure which in conjunction with said compression spring forces the chamber end of said probe to encircle the inlet port and bear upon the cylinder end face.

References Cited by the Examiner UNITED STATES PATENTS 2,190,755 2/1940 Dinzl 91-441 2,250,389 7/1941 Miller 91--6 2,633,708 4/1953 Sedgwick 91-16 2,805,447 9/1957 Voges 91-441 MARTIN P. SCHWADRON, Primary Examiner.

SAMUEL LEVINE, Examiner. 

1. A LINEAR ACTUATOR OF THE DISPLACEMENT TYPE COMPRISING A CYLINDER MEMBER AND A COACTING PISTON-AND-ROD MEMBER DEFINING A HYDRAULIC FLUID CHAMBER THEREBETWEEN, MEANS IN ONE END FACE OF SAID CHAMBER DEFINING AT LEAST ONE BORE OPENING THROUGH SAID END FACE INTO SAID CHAMBER AND EXTENDING LONGITUDINALLY IN A DIRECTION PARALLEL TO THE ACTUATOR AXIS, AN OPEN-ENDED GENERALLY-TUBULAR PROBE FREELY-SLIDABLY MOUNTED IN SAID BORE AND CAPABLE OF BEING SUBSTANTIALLY FULLY RECEIVED THEREIN, THE END OF SAID BORE AND SAID PROBE DEFINING A PROBE POCKET THEREBETWEEN MEANS FOR ADMITTING PRESSURIZED HYDRAULIC FLUID INTO SAID CHAMBER DISPOSED IN THE OPPOSITE CHAMBER END FACE THROUGH WHICH HYDRAULIC FLUID CAN BE FED INTO AND THROUGH SAID OPEN-ENDED PROBE, AND MEANS FOR ADMITTING HYDRAULIC FLUID TO SAID CHAMBER AND FOR EXHAUSTING IT THEREFROM ON ADVANCE AND WITHDRAWAL OF THE ACTUATOR RE- 